The development of automatic CNC grinding technology has raised high requirements for its supporting equipment. As one of the supporting technologies, the online automatic grinding wheel dressing technology must meet the needs of modern CNC grinding technology and make it develop towards the direction of high precision, super stability and full self-control.
As a high efficiency grinding tool, diamond grinding wheel is widely used in the processing of hard alloy, ceramics, CBN and other superhard materials. The dressing and automatic compensation method of diamond grinding wheel determine the performance of automatic CNC grinding machine, which largely determines the performance and service life of the grinding wheel.

Principle of diamond grinding wheel dressing

The dressing method of diamond grinding wheel is an important factor that affects the grinding performance of the grinding wheel. At present, the common dressing methods of diamond grinding wheel are: on-line electrolysis dressing, EDM grinding wheel dressing, cup grinding wheel dressing, electrolysis - mechanical compound dressing and laser dressing. Because the dressing method of cup grinding wheel is simpler and easier to realize than other dressing methods, GC cup grinding wheel dressing technology is adopted in this paper for automatic dressing of diamond grinding wheel. The dressing of diamond grinding wheel is usually divided into two stages: shaping and sharpening. The purpose of shaping is to remove the shape error and surface defect of the grinding wheel after the initial installation and ensure the geometric shape accuracy of the grinding wheel. Sharpening is due to the grinding wheel after working for a period of time passivation, in order to make the cutting edge of the bond prominent and appropriate height, the formation of enough chip space between the grinding grains, and make the effective number of grinding grains per unit area as much as possible.

A method for dressing the cup - shaped diamond wheel with GC cup - shaped grinding wheel

In actual dressing, the grinding belt of the bowl diamond grinding wheel and the GC cup grinding wheel are completely staggered and fitted, which are rotated at a certain speed respectively. The rotational linear velocity ratio of the dressing wheel and the grinding wheel is 8:1. The dressing wheel is fixed, and the diamond grinding wheel is dressed and fed along the axis, so that GC cup grinding wheel and bowl diamond grinding wheel can form mutually unabrasive grinding. By grinding the end faces of the two grinding wheels, the passivated grinding grains of the diamond grinding wheel are removed to form a chip space, and the surface of the diamond grinding wheel is re-sharpened to achieve the purpose of dressing.

Automatic control method of grinding wheel dressing

In grinding, the wear state of the grinding wheel is an important factor that affects the grinding quality. The CNC tool grinder can monitor the status of grinding wheel in real time during the whole process of blade grinding. Depending on the size of the machining blade and the material, the volume and grinding time needed to be removed also vary. Take all factors into consideration and set the interval of automatic dressing. By counting the number of grinding blades with the grinding wheel and comparing it with the dressing interval set by the system in real time. When the grinding times reach the set dressing interval times, the dressing module is automatically called in the NC program to realize the automatic dressing of the grinding wheel. In order to ensure the safety of machine operation, the control method also adds real-time monitoring of grinding wheel life and dressing wheel life. As long as it is detected that this dressing may cause the grinding wheel or dressing wheel to reach the pre-warning thickness, the machine will automatically send an alarm signal and stop the machine for manual processing. If the grinding wheel and dressing wheel do not reach the alarm thickness, the dressing will proceed smoothly. After finishing dressing, the compensation value after grinding wheel dressing is output through data processing.

Compensation method for grinding wheel dressing

The consistency of the size of the workpiece is largely determined by the consistency of the state of the process system. After the grinding wheel is dressed once, the thickness of abrasive decreases and the end face of the grinding wheel changes to the designated calibration position, which results in the change of the state of the whole process system and the size of the workpiece being processed, so the size consistency cannot be guaranteed. Therefore, compensation after grinding wheel dressing is particularly important. Analysis of the grinding wheel dressing process is the mutual grinding of two grinding tools, which not only reduces the grinding wheel abrasive thickness, but also reduces the grinding wheel abrasive thickness, which is the result of a comprehensive effect. Therefore, the compensation method of grinding wheel dressing is determined by multiple tests. The hardness and wear resistance of diamond grinding wheel is much higher than that of GC cup-shaped dressing wheel. It can be predicted that during a dressing process, the abrasive thickness reduced by diamond grinding wheel is much smaller than that reduced by dressing wheel. The position of dressing wheel is fixed. During dressing, the grinding wheel advances a dressing amount along the feed direction. Due to the mutual grinding effect, the thickness of the grinding wheel and dressing wheel decreases simultaneously. The relationship between them is: dressing amount = reduction of grinding wheel = reduction of dressing wheel. In order to ensure the dimensional consistency of the workpiece to be machined, the reduction of grinding wheel after dressing should be compensated. The actual dressing test data show that when the dressing quantity is 0.03mm, the thickness reduction of grinding wheel is 0.0015mm and that of dressing wheel is 0.0275mm.

Conclusion

The automatic control method and compensation method of grinding wheel dressing have been applied in the tool grinder developed by the project. Through continuous test grinding for a long time, the dimension consistency of the workpiece processed by the machine is controlled within 5 m, and the practical effect of this method is verified.